Temperature can be used to control and change one or more reaction rates in (bulk) chemical conversion processes. For example, heating is often used to increase a reaction rate. On the other hand, in case of a thermally labile catalyst, such as an enzyme, heating can also be used to decrease a reaction rate. Accordingly, precise control of the temperature of a bulk chemical reaction mixture is often required to control one or more reaction rates. In addition, high pressure is often applied to obtain a sufficient reaction rate for gas phase reactions.
Conventional heating methods do not allow for near instantaneous, fast and/or local heating of components of a fluid phase. For instance, heating a liquid at 75° C. for only one second is difficult using conventional means. In addition, chemically selective heating, i.e. providing thermal energy from an external source to one or more selected components of a fluid mixture is difficult using conventional means. For example, it is difficult to selectively heat enzymes in a liquid, which would be render them inactive.
Most research on plasmonic particles, such as noble metal nanoparticles, has focussed on their optical properties, in particular their enhanced scattering. The enhanced light absorption and associated heating of such particles were considered as (mostly unwanted) side effects in plasmonics applications. Only recently it has been sought to use plasmonic particles as heat source. Applications are mostly in biomedicine, for example in photo-thermal cancer therapy and bio-imaging.
Steam reforming of ethanol inside a micro-channel using plasmonic heating by gold nanoparticles has been described by Adleman et al. (Nano Letters 2009, 9, 4418-4423). A laser (50 mW, 10±2 μm diameter) at or near the frequency of the plasmon resonance (532 nm) of ˜20 nm gold nanoparticles is focused on the top of a glass support, and the subsequent heat generated in the nanoparticles is transferred to the surrounding fluid which forms a vapour. The vapour phase components react forming gas bubbles which are carried downstream in a microfluidic 40 μm height glass/polydimethylsiloxane (PDMS) channel. The particles are attached to a glass support.
Neumann et al. (ACS Nano 2013, 7, 42-49) describe solar vapour generation using broadly absorbing metal or carbon nanoparticles dispersed in a liquid phase. They report an increase of the surface temperature of the nanoparticles above the boiling point of the liquid. Vapour that formed around the nanoparticles resulted in bubbles composed of nanoparticles enveloped by a vapour shell. The bubbles, comprising nanoparticles, moved to a liquid-air interface where steam was released. They also describe distillation of ethanol-water mixtures (20 ml) with Au nanoshell particles in dispersion (2.5×1010 particles/ml) using focused sunlight. In this document, particles are separated from an evaporated compound rather than a liquid component.
US-A-2008/0 154 431 to Defries describes means to use at least a form of light-matter interaction, to generate localised conditions that enable initiation of chemical reactions. It mentions a strong interaction of light with a metallic nanoparticle. The temperature of the nanoparticle is raised. A method is described incorporating metallic nanoparticle catalyst and the use of light-matter interactions to control localised thermal conditions to control catalytic chemical reactions including polymerisation.